全文获取类型
收费全文 | 195918篇 |
免费 | 24738篇 |
国内免费 | 17462篇 |
专业分类
化学 | 113483篇 |
晶体学 | 2921篇 |
力学 | 9788篇 |
综合类 | 25篇 |
数学 | 21790篇 |
物理学 | 90111篇 |
出版年
2020年 | 1457篇 |
2019年 | 1950篇 |
2018年 | 1955篇 |
2017年 | 2544篇 |
2016年 | 3368篇 |
2015年 | 3278篇 |
2014年 | 3441篇 |
2013年 | 8692篇 |
2012年 | 7503篇 |
2011年 | 10031篇 |
2010年 | 11657篇 |
2009年 | 11691篇 |
2008年 | 7130篇 |
2007年 | 6717篇 |
2006年 | 6477篇 |
2005年 | 6757篇 |
2004年 | 7160篇 |
2003年 | 6089篇 |
2002年 | 5827篇 |
2001年 | 6561篇 |
2000年 | 4886篇 |
1999年 | 4598篇 |
1998年 | 3937篇 |
1997年 | 3741篇 |
1996年 | 3975篇 |
1995年 | 4339篇 |
1994年 | 4196篇 |
1993年 | 4280篇 |
1992年 | 4070篇 |
1991年 | 3694篇 |
1990年 | 3334篇 |
1989年 | 3403篇 |
1988年 | 3410篇 |
1987年 | 2753篇 |
1986年 | 2699篇 |
1985年 | 2961篇 |
1984年 | 3187篇 |
1983年 | 2247篇 |
1982年 | 3058篇 |
1981年 | 2729篇 |
1980年 | 2815篇 |
1979年 | 2577篇 |
1978年 | 2696篇 |
1977年 | 2708篇 |
1976年 | 3100篇 |
1975年 | 2234篇 |
1974年 | 2075篇 |
1973年 | 2532篇 |
1972年 | 1782篇 |
1971年 | 1384篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Andrew W. Sale 《Geometriae Dedicata》2015,176(1):305-313
32.
Kinetics and Catalysis - A series of Cu-SSZ-13@CeO2 catalysts with surface modification with CeO2 was prepared by the modified self-resemble method based on the one-pot synthesized Cu-SSZ-13... 相似文献
33.
34.
35.
Gas-phase 21Ne nuclear magnetic resonance spectra were measured at the natural abundance of 21Ne isotope for samples consisting of pressurized neon up to 60 bar at room temperature and applying the magnetic field of the strength B0 = 11.7574 T. It showed that the nuclear magnetic resonance frequency is linearly dependent on the density of gaseous neon. The resonance frequency was extrapolated to the zero-density point, and it permitted the determination of the 21Ne nuclear magnetic moment, μ(21Ne) = 0.6617774(10) μN. The present value of μ(21Ne) is not influenced by the bulk magnetic susceptibility of neon and interactions between neon atoms; therefore, it is more precise and reliable than the previous result obtained for μ(21Ne). 相似文献
36.
Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface. 相似文献
37.
The existence and occurrence, especially by a backward bifurcation, of endemic equilibria is of utmost importance in determining the spread and persistence of a disease. In many epidemiological models, the equation for the endemic equilibria is quadratic, with the coefficients determined by the parameters of the model. Despite its apparent simplicity, such an equation can describe an amazing number of dynamical behaviors. In this paper, we shall provide a comprehensive survey of possible bifurcation patterns, deriving explicit conditions on the equation's parameters for the occurrence of each of them, and discuss illustrative examples. 相似文献
38.
39.
40.